1. Field of the Invention
This invention relates to a combustion turbine vane shroud assembly, and more specifically, to a combustion turbine vane shroud assembly comprising a plurality of adjacent vane assemblies and a cover element extending across a gap between adjacent vane assemblies for covering a portion of the vane assemblies and for limiting leakage of gases through the gap between the vane assemblies.
2. Background Information
Generally, combustion turbines have three main assemblies, including a compressor assembly, a combustor assembly, and a turbine assembly. In operation, the compressor assembly compresses ambient air. The compressed air is channeled into the combustor assembly where it is mixed with a fuel. The fuel and compressed air mixture is ignited creating a heated working gas. The heated working gas is typically at a temperature of between 2500 to 2900° F. (1371 to 1593° C.), and is expanded through the turbine assembly. The turbine assembly generally includes a rotating assembly comprising a centrally located rotating shaft and a plurality of rows of rotating blades attached thereto. A plurality of stationary vane assemblies including a plurality of stationary vanes are connected to a casing of the turbine and are located interposed between the rows of rotating blades. The expansion of the working gas through the rows of rotating blades and stationary vanes or airfoils in the turbine assembly results in a transfer of energy from the working gas to the rotating assembly, causing rotation of the shaft. A known construction for a combustion turbine is described in U.S. Pat. No. 6,454,526, which patent is incorporated herein by reference.
The vane assemblies may typically include an outer platform element or shroud segment connected to one end of an airfoil for attachment to the turbine casing and an inner platform element connected to an opposite end of the airfoil. The outer platform elements may be located adjacent to each other to define an outer shroud, and the inner platform elements may be located adjacent to each other to define an inner shroud. The outer and inner shrouds define a flow channel therebetween for passage of the hot gases past the stationary airfoils. The adjacent platform elements of the outer and inner shrouds generally abut each other along a junction where a gap may be formed, which may permit leakage of gases from the flow channel, and which may result in reduced efficiency of the turbine.
The first row of vane assemblies, which typically precedes the first row of rotating blades in the turbine assembly, is subject to the highest temperatures of the working gas, and therefore may be provided with a cooling system including passageways in the vane assembly for a cooling fluid. However, the surfaces of the vane assemblies exposed to the hot gases in the flow channel may be subject to burning and damage. The damage to a platform element of the vane assembly may require replacement of the entire vane assembly, even when the airfoil is still in a serviceable condition.
Accordingly, it is an object of the present invention to provide vane shroud assembly for a combustion turbine engine including a structure for sealing across a gap between adjacent vane assemblies. It is a further object of the invention to provide a replaceable structure for sealing across the gap between adjacent vane assemblies while also providing a covering over exposed surfaces of the vane assemblies.